The ability of paper or cardboard absorb water is an important property in order to determine the suitability of the paper or cardboard for different fields of use. The “Cobb value” of a paper is a measure of this ability to absorb water.
From a general point of view the Cobb method is carried out such that an area of 100 cm2 of a paper specimen during 60 seconds is subjected to influence from water, whereafter excess water is removed in a prescribed manner. Starting out from the weight of the paper before and after the exposure, the weight of the absorbed water is determined, which gives the Cobb value. A high Cobb value thus means that the water absorption ability is high and a low Cobb value that the water absorption ability is low.
The Cobb method (ISO 535) is a manual method which is slow, uncertain and labour-intensive and therefore costly. Because of the manual elements in the method, high accuracy on the side of the operator carrying out the method is required in order to avoid important erroneous measurements and thereby basically wrongful determinations of the ability of the paper to absorb water.
The Aim and most Important Features of the Invention
It is an aim of the present invention to provide a method and a device as mentioned above that eliminates the problem of the previously known manual method. In particular the invention aims to provide a secure, fast and economic method and a device which overcomes these problems.
These aims are obtained in respect of a method and a device as mentioned initially through the characterizing features of the independent claims.
Hereby is achieved that the change in the amount of liquid in the liquid chamber unit is used for calculating the amount of liquid that is absorbed in the material specimen. Manual sources of errors such as erroneously supplied amount of liquid, erroneously executed blotting etc. can be directly eliminated through the invention. In addition it is possible to automate the method. The time period thereof is then essentially only controlled by the time when the liquid is in contact with the surface of the specimen.
The invention is firstly intended for different types of measurements of the ability of paper to absorb not only water but also other liquids such as oils, solvents, impregnating agents etc.
The invention is also applicable for measurements on other surfaces, besides papers, such as plastics, textiles, wooden materials, surface coverings etc. for determining the ability of these materials to absorb different liquids.
In particular, and which is preferred, the liquid-contacting surface of the test specimen is brought to lie against one side of a rigid and water permeable wall of a main chamber of the liquid chamber unit. Hereby is avoided that possible wrinkling and other undesired movements of the test specimen affect the measuring results. in an erroneous direction. In particular it is preferred that the test specimen is pressed against said wall, for example by means of a flexible membrane or any other elastic means in order to further ensure the flatness of the test specimen and avoid movements of the test specimen during the measurement, inducing sources of errors.
In a preferred embodiment, the liquid chamber unit is connected to a sensor chamber wherein the liquid level is sensed. By forming the sensor chamber with an essentially smaller surface area than the surface area, with which the liquid contacts the material specimen, an amplified level change in the sensor chamber is achieved during the process of the measurement, also in case of relatively low liquid absorption, which increases the precision in the measurement.
By the test specimen being sealingly clamped against a housing portion including the liquid chamber unit, leakage as a source of errors is prevented.
Corresponding advantages are obtained with the corresponding features of a device for measuring according to the invention.